The present invention relates to a cruise control apparatus for a vehicle which serves to maintain the speed of the vehicle at a constant value in an automatic fashion.
FIG. 9 shows the general arrangement of a conventional cruise control apparatus for a vehicle as disclosed in Japanese Patent Laid-Open No. 58-39311. In this figure, a set switch 1 is adapted to be manipulated by the driver of the vehicle to start cruise control. A cancellation switch 2 is turned on in response to the application of the brakes by the driver to cancel the cruise control. A speed sensor 3 senses the speed of the vehicle, and comprises a cruciform rotary member 3a which has four magnetic poles equally spaced from each other at an interval of 90 degrees and which is rotated by an unillustrated transmission through an unillustrated metering cable, and a reed switch 3b disposed near the rotary member 3a so that it is open or closed each time one of the four magnetic poles comes in proximity of the reed switch 3b for generating a pulse signal in the form of a series of pulses having a frequency proportional to the speed of the vehicle. A power source in the form of a battery 4 is connected through a power or main switch 5 to a control unit 6 including a computing and processing circuit 6a such as a microcomputer, so that the control unit 6 is powered by the battery 4 when the main switch 5 is turned on. The control unit 6 receives the output signals from the set switch 1, the cancellation switch 2 and the speed sensor 3. Based on these signals, the control unit 6 performs various operational calculations for automatically controlling the speed of the vehicle so as to make it equal to a target speed V, and generates various output signals for automatic cruise control. A throttle actuator 7 in the form of a motor-operated actuator having an unillustrated motor is electrically connected to the control unit 6 so that it receives the output signals from the control unit 6 for driving a throttle valve 9 in a closing or opening direction. The throttle valve 9 is disposed in an intake pipe 8 of the engine and it is connected to an unillustrated accelerator pedal through an unillustrated cable or the like so that it is caused to rotate around a pivot shaft by an accelerator pedal operation of the driver through the cable for controlling the amount or flow rate of intake air supplied to the engine via the intake pipe 8. The throttle actuator 7 is operatively connected to the throttle valve 9 through a link member 7a and a connecting rod 7b, so that the link member 7a is caused to rotate around its pivot axis under the action of the motor in the throttle actuator 7 to drive the throttle valve 9 via the rod 7b. The unillustrated motor of the throttle actuator 7 is operatively coupled with the link member 7a through an unillustrated electromagnetic clutch which is operated by an electromagnetic clutch operating signal from the control unit 6 to control the mechanical connection between the motor and the link member 7a.
The operation of the above-mentioned conventional cruise control apparatus will now be described in detail below. When the main switch 5 is turned on by the driver, the control unit 6 is powered by the battery 4 and processes the output signal from the speed sensor 3. The speed sensor 3 generates a speed signal comprising a series of pulses having a frequency proportional to the speed at which the vehicle is travelling. The control unit 6 measures the periods of successive pulses and calculates the vehicle speed based thereon. In this state, if the driver manipulates the set switch 1, a corresponding signal is sent therefrom to the control unit 6 which then stores the vehicle speed at that time as a target speed, while starting cruise control. Thereafter, the control unit 6 successively compares the actual speed of the vehicle successively detected with the target speed and generates control signals to the throttle actuator 7 which is thereby operated to properly control the opening of the throttle valve 9 in order to make the vehicle travel at the target speed. Specifically, if the actual vehicle speed is lower than the target speed, the control unit 6 generates a throttle-opening signal for opening the throttle valve 9 by a predetermined quantity, whereas if the vehicle speed is higher than the target speed, the control unit 6 generates a throttle-closing signal for closing the throttle valve 9 by a predetermined quantity. As a result, the vehicle can travel at the constant target speed in an automatic fashion without the need of the driver's accelerator pedal operation.
If the driver applies the brakes of the vehicle during such cruise control, the cancellation switch 2 is operated, generating a cruise cancellation signal to the control unit 6. Upon receipt of the cancellation signal, the control unit 6 immediately generates a clutch releasing signal to the throttle actuator 7 which then disengages the unillustrated electromagnetic clutch. Thereafter, the driver can control the vehicle speed at his or her own will by stepping down or up the accelerator pedal to manually adjust the opening of the throttle valve 9.
With the conventional cruise control apparatus as constructed above, the control unit 6 successively makes a comparison between the varying actual speed of the vehicle and the target speed at predetermined time intervals measured by a timer or when a deviation between the actual vehicle speed and the target speed exceeds a predetermined value without regard to the slope of the road, the weight of the vehicle, etc., so that it generates a control output to the throttle actuator 7 for making the actual vehicle speed equal to the target speed, whereby the throttle actuator 7 can properly control the opening of the throttle valve 9. However, this results in the following drawbacks. Namely, when the vehicle is travelling on an uphill slope, the transmission can be forced to frequently perform shift-up and shift-down operations, or when the vehicle is travelling on a downhill slope, the transmission can be controlled to continuously shift down, thus preventing proper or necessary speed control.